A fan is a main heat dissipation tool for a wide range of consumption products. When a consumption product has a system temperature that is too high, the fan mounted in the consumption product will be automatically actuated to lower the overall system temperature and achieve the purpose of heat dissipation. On the other hand, when the system temperature has lowered to a specific value, the fan will stop operating automatically. Conventionally, to prevent the consumption product from becoming burned-out due to an overheated system, a cooling fan is mounted in the system as an overheat protection. However, since most of the currently available consumption products include electronic elements that compute at a speed much higher than before and accordingly produce more heat during operation, the fans designed for these consumption products must also have a largely increased rotation speed to timely remove the large amount of heat produced by the electronic elements. Under this circumstance, even when the fan has been turned off, it will keep rotating inertially for a short period of time before it fully stops.
Presently, the braking of conventional DC (direct-current) fans is mainly achieved through circuit board design, and can be generally divided into two modes. The first mode of fan braking is known as “turn-on braking”, which is performed via software processes. When the fan is turned on, a microcontroller unit (MCU) of the fan controls an H-bridge motor driving circuit for two lower MOS transistors (metal-oxide-semiconductor transistors) to be normally opened, so that the blades of the fan rotate to produce a magnetic field, which interacts with the magnetic field produced by a magnetic strip to thereby generate a resistance and achieve the braking effect. The second mode of fan braking is known as “turn-off braking”, which is performed via hardware. For example, a capacitor energy storage device is used to supply power to the H-bridge motor driving circuit of the fan when the fan is turned off, so that the two lower MOS transistors are normally opened to form a short circuit at two ends of the H-bridge that are connected to a motor coil of the fan. At this point, since the motor poles are prevented from producing any change, it is able to achieve the braking effect.
In summary, according to the conventional fan braking techniques, either an additional braking circuit must be provided on the original fan circuit board or an MCU with a braking-mode function must be installed in the fan to achieve the braking effect. However, the conventional fan braking modes based on circuit design can only bring the rotating fan blades to stop rotating gradually instead of quickly stopping the blades. Further, it is known the printed circuit boards of all types of fans already have wirings and circuits provided between various electronic elements for intended functions and has not extra space for directly forming additional fan braking circuits thereon. That is, the manufacturers have to use a new circuit board and modify the original fan circuit design to allow the provision of the additional fan braking circuit on the circuit board. In other words, the conventional fan braking modes have low compatibility with existing fans.